Bleeping Computer
Hackers have launched a massive attack against more than 900,000 WordPress sites seeking to redirect visitors to malvertising sites or plant a backdoor if an administrator is logged in.
Based on the payload, the attacks seem to be the work of a single threat actor, who used at least 24,000 IP addresses over the past month to send malicious requests to more than 900,000 sites.
XSS, malvertising, backdoor
Compromise attempts increased after April 28. WordPress security company Defiant, makers of Wordfence security plugin, detected on May 3 over 20 million attacks against more than half a million websites.
Ram Gall, senior QA at Defiant, said that the attackers focused mostly on exploiting cross-site scripting (XSS) vulnerabilities in plugins that received a fix months or years ago and had been targeted in other attacks.
Redirecting visitors to malvertising is one effect of a successful compromise. If the JavaScript is executed by the browser of an administrator that is logged in, the code tries to inject a PHP backdoor in the theme’s header file along with another JavaScript.
The backdoor then gets another payload and stores it in the theme’s header in an attempt to execute it. “This method would allow the attacker to maintain control of the site” Gall explains.
This way, the attacker could switch to a different payload that could be a webshell, code that creates a malicious admin or for deleting the content of the entire site. In the report today, Defiant included indicators of compromise for the final payload.